Abstract

Keeping in view the future in situ space applications, to study planetary surface science, we have designed and developed an impedance-based extremely compact wireless sensor node to infer the presence of water/ice in a soil sample and reported in this paper. Although reflectometry-based soil moisture sensors are available commercially, they have slightly longer probe, needing more volume, from the payload point of view. The reported wireless impedance sensor reproduced in space-qualified form can be useful to measure the permittivity of lunar regolith and infer the presence of water ice. It works in the frequency domain with capability to sweep the frequency in a given measurement range. The sensor does not necessarily have long probe, and it needs only electrical contact with the soil surface, thus eliminating extra energy for insertion by the rover on the lunar surface, in one of its possible space applications. The sensor has been made to operate in wireless mode, which is a basic need in any space applications. The data are transmitted at 2.4 GHz to the aggregator. We have tested sand-type terrestrial soil and lunar soil simulant JSC-1A. To verify the performance of the sensor, we have also tested Milli-Q water. All these experimental results are reported in this paper. Results of Milli-Q water, whose permittivity is known, agree with those reported in the literature, verifying excellent performance of the sensor. Thus, the sensor can be very useful for space applications, where size and weight are critical issues. A wireless impedance sensor can also be quite useful for terrestrial applications, for example, in agriculture, and also in other impedance-based applications